The present invention is generally related to controlling and tracking access to various types of objects. More particularly, the present invention relates to an object control system for continuous inventory of a plurality of objects.
Systems have been developed in which a user swipes an optical bar code on a key tag before placing the key tag in a slot or on a peg of a storage unit. A switch associated with the slots or pegs of the storage unit detects that a tag has been placed in a specific slot, or on a specific peg. In these systems, a connected controller assumes, but does not know with certainty, that the user has placed the swiped tag in the slot or on the peg. The shortcoming of this system, of course, is that the identification of the tag placed in a slot, or on a peg, is dependent upon the integrity of the user. A user can, for example, swipe one tag and place another tag in the slot or on the peg and the controller has no way of knowing of the deception or error. Thus, the system is not completely secure.
Other systems have been developed in which the identification of tags present in a receptacle is determined by communicating with the tags in the receptacle via infrared signals. In these systems, the controller knows that a tag is in the receptacle but cannot know the particular slot of the receptacle occupied by the tag. Light emitting diodes (LEDs) are provided on each tag to identify a requested tag visually to a user requesting the key associated with the tag, such that the particular slot associated with each tag is not deemed to be critical. The shortcomings of such a system include the fact that the system can not identify the specific location of each tag within the receptacle. Similar systems have been developed wherein each tag includes an addressable switch, and an LED on the tag lights when the ID code of the particular tag within the receptacle is transmitted by the controller. In these systems, as well, the controller can never identify the specific location of a tag within the receptacle.
The inventor""s previous object tracking patents, U.S. Pat. Nos. 5,801,628 and 6,075,441, used one-wire memory buttons on key tags as a preferred embodiment. The presence of a key tag in a key tag slot was determined by selectively polling each slot location using a matrix selector. In addition to determining the presence of a key tag, the one-wire memory buttons have unique identification (ID) codes that allow the key control system to identify which key tag is inserted in each slot. The inventor""s prior RF key control system patent, U.S. Pat. No. 6,204,764 used radio frequency identification (RFID) tags on key tags. At each tag slot, an RFID sensor antenna was placed to communicate, and again, a matrix selector approach was used to poll each slot. Because the RFID tags contain unique ID codes, this system also determines presence and identification in the same process.
Although these object tracking systems are sophisticated and provide a continual inventory of a plurality of objects, separation of the identification function and the location/detection function can result in novel key control systems. These novel systems offer the potential to be technically simpler and thus available at lower costs.
The present invention separates the object identification function and the object location detection function in a key control system. More generally, the present invention provides an object control and tracking system and related methods that use separate object identification and location detection mechanisms for objects, that are maintained in a secure enclosure. A plurality of object slots that are xe2x80x9celectrically smallxe2x80x9d in comparison to the wavelength of the RFID sensors are located on the top tray of the enclosure to receive object tags that include both an RFID tag and an object to be tracked. The objects are attached to a portion of the object tags that are outside of the enclosure. Presence detectors positioned on the backplane of the enclosure are used to determine if an object tag is present in the corresponding slot of the enclosure. RFID sensors located on opposite interior side walls of the enclosure interrogate each RFID tag to determine the presence of each RFID tag within the enclosure. Each RFID tag includes an anti-collision protocol to enable a plurality of RFID tags within the sensor field to be interrogated. In one embodiment, the RFID sensors include a pair of sensor coils and the RFID tags are inductive. The pair of sensor coils generate a magnetic field between the side walls of the enclosure, the magnetic field being normal to the vertical surface of each object tag. In another embodiment, the RFID sensors include capacitive plates, and the RFID tags are capacitive. The object control enclosure is constructed of metal and is shielded to prevent detection of object tags that are located externally to the enclosure and that could be contained in a separate object control enclosure.
The object control and tracking system includes a processor, a memory for storing an object control database, and related processing logic operating on the processor to control scanning of the presence detectors to determine if an object tag is present in a corresponding slot, to identify each object (via its unique RFID tag) present in the enclosure and to compare the identified objects with an object control database to determine each object removed or replaced since the previous database update.
Various types of switches mounted on the backplane are suitable for use as object tag presence detectors. These include a contact switch having a lever that is engaged to close the contact switch when an object tag is inserted into a corresponding slot. Another suitable switch includes a photo-conducting switch mounted to the backplane on a side of a corresponding slot with a light emitting diode mounted on the opposite side, such that insertion of the object tag into the slot causes an electrical circuit to open to indicate the presence of an object tag. The object tag can also include a metallic end portion or an embedded magnetic material that causes an electrical circuit to close when either an object tag is inserted into the corresponding slot and is detected by engaging a pair of contacts in the slot or when a reed switch is energized by proximity of the object tag.
In one embodiment, each object tag includes a light emitting diode circuit, an RFID addressable switch and an RFID tag coil. An RFID addressable switch enables an RFID interrogating field to selectively activate a light emitting diode on the object tag corresponding to the object a user is trying to identify in order to remove the object from the enclosure.